Cellulosic flame retardant system

ABSTRACT

A process for imparting flame retardant character to cellulosic containing materials has been devised in which the cellulosic material is treated with an aqueous solution of further polymerizable methylol-phosphorus compound obtained by reacting a tetrakis(hydroxymethyl)phosphonium acid salt e.g., tetrakis(hydroxymethyl)phosphonium chloride with about 0.5 to 1.5 mol proportion of ammonia, in the presence of a carbamic acid derivative, e.g., urea, and the treated material is contacted with an aqueous solution of ammonia thereby curing the methylolphosphorus-compound in and on the cellulosic material.

United States Patent 1191 1111 3,784,356 Wagner 7 1 51 Jan. 8, 1974CELLULOSIC FLAME RETARDANT 3,247,015 4/1966 Zimmerman et al. 117/136 x SSTEM 2,772,188 11/1956 Reeves et a1 117/136 I 3,236,676 2/1966 Coates eta1. 117/622 [75] Inventor: George M. Wagner, Lew1ston, NY. [73]Assignee: Hooker Chemical Corporation, Primary Guynn Ni FalAttorney-Peter F. Casella et al.' [22] F11ed: Nov. 10, 1971 ABSTRACT[21] Appl' 1 7 A process for imparting flame retardant character tocellulosic containing materials has been devised in 52 US. (:1. 8/196,8/116 P, 8/120, which h cellulosic material is treated h aque 8/181 117/622, 1 17/136 one solution of further polymerizable methylol- 51 Int.Cl D06m 13/44 Phosphorus compound Obtained by reacting a tetrakis- [58]Field of Search. 8/1162, 116 P, 181, (hydroxymflthyl)ph'osphonihm acidsalt s tetrakisb 8/196; 117/136, 622 hydroxymethyl)phosphoniumchloridewith about 0.5 to 1.5 mol proportion of ammonia, in the presence of 5References Cited a carbamic acid derivative, e.g., urea, and the treatedUNITED STATES PATENTS material'is contacted with an aqueous solution ofam- 2 983 623 5,196 C /6 2 monia thereby curing themethylol-phosphorusoates 3,276,897 10/1956 Reeves et al.... 117/136compound m and on the celluloslc mammal. 3,404,022 10/1968 Chance et al117/136 X 11 Claims, No Drawings 1 CELLULOSIC FLAME RETARDANT SYSTEMBACKGROUND OF THE INVENTION I The treatment of cellulosic containingmaterials to impart flame retardant character thereto has been thesubject of considerable effort and many such processes have beenproposed. However, most if not all such processes have defects whichmilitate against their complete acceptance by those working in thisarea.

It is known, according to U.S. Pat. No. 2,772,188 to utilize an aqueoussolution ofa further polymerizable methylol-phosphorus compound to treata cellulosic containing material, and after drying the treated material,to react the methyloi-phosphorus compound with ammonia, in gaseous ordissolved state to insolubilize US. Pat. No. 2,983,623 discloses animprovement in .the aforementioned process whereby the dried cellulosematerial impregnated with the methylolphosphorus compound is given aninitial treatment with gaseous ammonia and thereafter treated withaqueous ammonia.

In US. Pat. No. 3,096,20l it is shown that by including a substantialamount of 'diammonium sulfite in the methylolphosphorus compoundsolution, the gaseous ammonia treatment of the dried impregnatedcellulose material is rendered unnecessary.

According to US. Pat. No. 3,236,676, a cellulosic material is treatedwith an aqueous solution of a phosphonium compound, the material isdried and then heated at 100 to 180 C. to fix the phosphonium compoundon the material. The thus treated material is exposed to gaseous ammoniaand then treated with aqueous ammonium hydroxide to cure the phosphoniumcompound on the cellulosic material.

All these prior art processes have not been completely satisfactory forone or more reasons. For example, in many instances it has been observedthat the phosphonium. compound has a tendency to migrate to the surfaceof the material during the aqueous ammonia treatment and thus does notbecome permanently fixed to the fiber. During this aqueous treatment aconsiderable portion of the phosphonium compound is leached from thematerial or is polymerized on the surfaceof said material. It is knownalso that the reactionof gaseous ammonia with the phosphonium compoundis limited: by the rate of diffusion of the ammonia through the fabricwhich at times may be very low and in some instances the impregnatedmaterial must be maintained for long periods in the ammonia atmospherein order toobtain a fully reacted product. Moreover, the reaction beingexothermic in character, the temperature of the cellulosic material insome instances may get undesirably high. Also, the heating of the driedmaterial to fix the phosphonium compound on the material: is anadditional processing step requiring the expenditure of time and capitaland often results in the tendering or otherwise depreciating thephysical character of the treated cellulosic materials.

It can therefore be seen that the prior art methods proposed for theapplication of phosphonium compounds to cellulosic materials leavessomething to be desired.

OBJECTS OF THE INVENTION It is therefore a principal object of thisinvention to devise a process for imparting flame retardancy tocellulose containing materials which; does not involve a step oftreating the material with gaseous ammonia.

Another object is to devise a simple, effective, and

economical process for treating cellulose containing.

materials with aqueous solutions of phosphonium compounds to render suchmaterials'flame retardant.

Other objects will be obvious'from the following description of thisinvention.

BRIEF DESCRIPTION OF THE INVENTION In accordance with the presentinvention, cellulose containing materials are treated with an aqueoussolution of a further polymerizable rnethylol-phosphorus compound, e.g.,tetrakis(hydroxymethyl)- phosphonium chloride, which has been reactedwith about 0.5 l.5 molar proportion of ammonia in the presence of atleast about 0.25 mole of carbamic acid derivative to form a watersoluble reaction product, and the treated material, preferably afterbeing partially dried, is contacted with a dilute aqueous solution ofammonia to cure the methylol-phosphorus compound in and on the cellulosecontaining material.

By this process, the steps of fixing the methylolphosphorus compound onthe material, and treatment of the impregnated material with gaseousammonia and with heat are avoided.

The process of the present invention is adaptable to the treatment ofcellulose containing materials such as cotton, regenerated cellulose,mixtures of these materials with synthetic materials such aspolyester-cotton blends, wood, paper, and the like.

DETAILED DESCRIPTION OF THE INVENTION In accordance with a preferredmode of carrying out the process of the present invention, an aqueoussolution of a tetrakis-(hydroxymethyl)phosphonium acid salt is reactedwith from about 0.5 to about 1.5 molar proportions of ammonia in thepresence of from about 0.25 to about 2 molar proportions of urea, whilemaintaining the pH of the solution below about 3. The resulting solutionis adjusted to a pH within the range of about 4 to 7 and preferably fromabout 5 to 6 by the addition of an alkaline agent, such as sodiumhydroxide, triethanolamine and the like. Thereafter, the solution ispadded onto a cellulosic containing material and the thus treatedmaterial is preferably dried to at least about a 50 percent moistureretention. This drying step is effected at a relatively moderatetemperature, such that no substantial fixation of the phosphoniumcompound on the material occurs. The dried material is thereaftercontacted with, e.g., padded with, a dilute aqueous ammonium hydroxidesolution to cure the phosphonium compound on and in the material. Thematerial is scoured in an aqueous alkaline bath containing a oxidizingagent, e.g., sodium peroxide, hydrogen peroxide, and the like, and thescoured material is rinsed and dried.

The resultant material is flame retardant and can be washed numeroustimes with soap/soda ash solutions at the boil without substantial lossof flame retardant character. Substantially no leaching or migration ofthe phosphonium compound occurs during the curing step.

Various acid salts of the tetrakis(hydroxymethyl)- phosphonium compoundare suitable for use in this invention. Exemplary of such salts are thechloride, bromide, sulfate, phosphate, acetate, and propionate. Thechloride, because of its general availability and overall effectivenessis the preferred salt.

Any of the further-polymerizable methylolphosphorus materials referredto in the aforementioned U.S. Pat. No. 2,772,188 are suitable for use inthe process of this invention. A particularly useful and hence preferredmaterial is tetrakis(hydroxymethyl)- phosphonium acid salt andespecially, the chloride. This salt reacts with limited amounts ofammonia to give a reaction product which is soluble and which isprobably a mixture of the mono-functional and bifunctional derivatives.As is known, when an excess of ammonia is used the phosphonium compoundreacts to give a trifunctional cross linked polymeric reaction productwhich is insoluble in water. However lesser amounts, i.e., amountswithin the range of about 0.5 to about 1.5 mols per mol of phosphoniumcompound result in reaction products which are water soluble andprobably comprise essentially mixtures of the monoand di-functionalderivatives. Further additions of ammonia to this reaction productresult in the formation of the insoluble, trifunctional cross linkedpolymer.

Carbamic acid derivatives which can be used in preparing the furtherpolymerizable phosphonium saltammonia reaction product include by way ofexample urea, thiourea, biuret, guanidene, cyanamide, dicyanamide,ethyleneurea, and the like. Of these, urea and thiourea are preferred.It isbelieved that the product formed by reaction of the phosphoniumsalt and ammonia in the presence of the carbamic acid derivative is arelatively stable, soluble complex which is decomposed during the dryingand/or curing steps liberating the carbamic acid derivative. Thecarbamic acid derivative is leached out of the impregnated material andthus does not remain, to any substantial amount, affixed to the treatedmaterial.

The amount of carbamic acid derivative used can be varied over aconsiderable range. Preferably this compound should be present in theamount of at least about 0.25 mole per mole of the phosphonium compound.Generally, it has been found that amounts of the carbamic acidderivative as great as 5.0 to 10.0 moles or more may be used, althoughamounts appreciably in excess of about two moles per mole of thephosphonium salt do not materially improve the results and hence forthis reason are not generally used.

Generally the pH of the aqueous solution of the reaction product of thephosphonium compound and ammonia is adjusted to within the range ofabout 4 to 7 and preferably within the range of about 5 to 6 prior to.

use although pH values outside of these limits can be used. As is known,strongly acidic media, i.e., media having a pH value below about 1 maydegrade cellulosic materials, while strongly alkaline media, i.e., mediahaving pH values above about 8 may result in undesirable decompositionof the phosphonium compound.

The pH of the aqueous solution can be adjusted to within the desiredrange by the use of alkaline agents such as sodium or potassiumhydroxides, sodium acetate, water soluble tertiary amines such astriethanolamine, tributyl amine, trihexylamine, triisopropanol 4 amine,tripentanolamine and the like. Of these alkaline agents, triethanolamineis preferred, and primary reference will be made hereinafter to thismaterial.

The aqueous solution can be applied to the cellulosic containingmaterial by conventional means such as by dipping, spraying, padding,and the like. The treated material can be passed through nip or squeezerolls to adjust the pickup of the solution to about percent on theweight of the material.

The drying of the impregnated material should be carried out underrelatively mild conditions, e.g., at temperatures of about degreescentigrade. Higher temperatures e.g., up to about to 200 degreescentigrade can be used, but care should be exercized that the materialis not heated in the dried condition to fix to any substantial degreethe resin on the material, for under such excess conditions oftemperature/time it has been found that the resinous materials have apronounced tendency to migrate to the surface of the material andproduce superficial resin coatings which are less fast to subsequenttreatments, such as washing, and produce unattractive spottiness on thematerial.

This drying operation is not considered essential to the process of thepresent invention. However, it has been observed that some leaching ofthe phosphonium salt-ammonia reaction product occurs when the materialis not dried. Thus it is preferred that the treated material be dried tothe extent of at least the removal of about 50 percent by Weight of itsmoisture content prior to curing. That is to say, it is preferred thatthe treated material be dried, under moderate conditions, to a moistureretention of 50 percent by weight or Ess.

Following this optional drying operation the treated cellulosic materialis subjected to a chemical curing operation, using a source ammonia. Theammonia may be supplied for this curing operation as aqueous ammonia,including ammonium hydroxide, solutions of amino compounds containing atleast two reactive hydrogen atoms per molecule, such as aminescontaining a primary amino group, hydrazine, alkyl substitutedhydrazines, and the like, ammonium carbonate, or other readilydissociated weak acid salts of ammonia, such as ammonium acetate,ammonium formate, and the like. Additionally, as disclosed in U.S. Pat.No. 3,310,419, the chemical cure of the treated cellulosic containingmaterial can be effected using a composition comprising a mixture of theammonium salt of a strong acid, such as ammonium sulfate, an alkalimetal carbonate, such as sodium carbonate, and an alkali metalbicarbonate, such as sodium bicarbonate. An aqueous solution of such amixture is prepared and the treated cellulosic containing material iscontacted therewith.

For ease of operation, it is generally preferred to effect the chemicalcure of the polymerizable compositio n wi th aqueous solutionsofarnmonia, containing about 3 to 10 percent ammonia. The chemical cureis carried out for a period of time sufficient to effect substantiallycomplete curing of the polymerizable composition in and on the materialwith the resulting substantially complete water insolubilization of thecomposition in and on the cellulosic material. While it is obvious thatthe exact time required for the chemical curing will vary, dependingupon the'amount of resin add-on to be obtained in and on the treatedmaterial, as well as the nature of the cellulosic material itself,chemical curing times of about one to about 5 minutes have been found tobe typical.

As with the treating and drying steps, the chemical curing operation mayalso be carried out in either mill apparatus or commercial laundryapparatus, depending upon the nature of the cellulosic-material beingtreated. Where yard goods are being treated, this curing operation canbe accomplished in a padder or on a jig. In mill set-ups, where thepadder is arranged in tandem relationship with the dryer, the chemicalcuring step can be carried out continuously. Where, however, thefinishing operations are to include a scouring in a jig, the ammoniacure is more conveniently carried out in jig during. the first end.

Th following examples will illustrate the process of the presentinvention. Parts and percentages are by weight and temperatures indegrees centigrade, unless otherwise specified.

Flame retardancies reported were determined in accordance with theprocedure of. the American Association of Textile Chemists andColorists, Test AATCC Base 34-1969. Tensile strengths were determined inaccordance with the procedure of Federal Specification CCCT-1916, 5100,and the stiffness of the fabric using a Gurley stiffness tester.

EXAMPLE 1 A solution of 500 parts of tetrakis(hydroxymethyl)-phosphonium chloride (80 percent 2.1 mols), and 60 parts of urea (1.0mol) in 315 parts of water was prepared The solution was agitatedvigorously as 125 parts of 28 percent ammonium hydroxide (2.06 mols NHwereadded dropwise in thirty minutes. The temperature of the mass roseto about 74 degrees and the pH was 2. The mixture was permitted to standat ambient temperature for about 24 hours, during which period thep Hdecreased to about 1.0.

Triethanolamine, parts, was added to 100 parts of the above preparedsolution to adjust the pHthereof to 5.0. The resulting solution was usedto pad a bleached cotton poplin, 5.5 oz per sq. yd. The materials wasrun through squeeze rolls to adjust the wet pick-up to about 100percent. The treated material was dried for two minutes at about 120degrees and then run through a 3 percent aqueous ammonium hydroxidepadding bath. The material was then scoured in an aqueous alkaline soapsolution containing 5 percent of 35 percent hydrogen peroxide to removeexcess chemicals, water-rinsed and the scoured material dried andconditioned at 21 and 65% RH. The dried fabric was found to haveincreased in weight by 18.9 percent compared to the original material.The treated material possessed excellent resistance to burning whentested by the conventional vertical strip flame test. This property wasnot impaired after subjecting the fabric to nine successive one hourboiling washes in a solution of 90 parts soap, 90 parts of soda ash, 10parts of a synthetic anionic detergent in about 50,000 parts of water.

EXAMPLE 2 This example illustrates the effect of varying the amount ofresin add-on on the permanance of the flame retardant character of thetreated material.

An aqueous solution containing the reaction product of one molproportion of tetrakis(hydroxymethyl)phosphonium chloride, (THPC) 0.8mol proportion of ammonia and 0.5 mol proportion of urea, was preparedas described in Example 1 above. Sample of 5.5 oz cotton poplin weretreated with this solution and thereafter the fabric was passed betweensqueeze rolls to obtain various levels of wet resin add-on. The treatedsamples were each dried for three minutes in a degree oven, cured byrunning through a three percent aqueous ammonia padding bath, scoured,rinsed and dried and conditioned at 21 degrees and65 percent relativehumidity. The treated samples were weighed to determine the amount ofresin add-on and then tested for flame retardance, initially and after 5and after'9 boil cycles as in Example 1. The tensile strength andstiffness were determined using the procedures: as have been indicatedherein above. The results'obtained are set out in the following Table.

LEGEND:

Based on THPC originally present in reaction mixture. 8" indicates thatthe sample burns. Tensile Strength of untreated material, fill 32lbs/in. warp 55 lbs/in.

These results indicate that whereas all the treated samples initiallywere rendered flame retardant, permanent flame retardance was obtainedonly after about 15 percent or more of the resin was added on thefabric. Moreover these data indicate that the treatment does notnoticeably affect either the tensile strength or stiffness of thefabric.

EXAMPLE 3 The importanceof the presence of the carbamic acid derivativein the aqueous solution of the reactionproduct is illustrated by thefollowing series of tests.

Aqueous solutions of the reaction product of one mol proportion oftetrakis(hydroxymethyl)phosphonium chloride and 0.8 mol proportionof'ammonia were prepared in the absence of, and in the presence ofvarious molar proportions of urea, as described in Example 1 above.Samples of 5.5 oz bleachedi cotton poplin material were treated withthis solution to a wet pick-up of 45 percent reaction product, thesamples dried at about 120 degrees for three minutes, cured with threepercent aqueous amrnonia, scoured. and conditioned as described inExample 2 aboverThe samples were then tested for flame retardance andthe results as set out in the following Table II.

1 Leaching is evidence by a pearance of whitejpolymer particles eitheron cloth or in ammonia curfiig bath.

2 3" indicates sample burns.

EXAMPLE 4 The effect of various amounts of ammonia used to form thereaction product of this invention is illustrated by the following.

One mol proportion of tetrakis(hydroxymethyl)phosphonium chloride wasreacted in the presence of 0.5 mol proportion of urea, with various molproportions of ammonia as described in Example 1 above.

The resulting aqueous solutions were used to treated cotton poplin andthe treated cloth processed as described in the above Example 1. Theresults obtained are set out in Table III below.

TABLE III Mols NHfl/Mol THPC 1.0 0.8 0.6 Reaction product on fiber wet45 45 45 Reaction product on scoured fiber l7.8 l9.5 15.0 Leaching NoneNone Slight Char length initial (in) 4.6 5.0 6.0 After 5 boil cycles(in) 4.9 4.5 4.6 After 9 boil cycles (in) 7.0 4.6 B

From the above results it can be seen that as the proportion of ammoniaused decreases below about 0.5 mol per mol of phosphonium salt, thereaction product becomes ineffective as an agent to impart fireretardance both with respect to leaching from the fabric and topermanance of the flame retardant character of the treated cellulosicmaterial.

EXAMPLE 5 This example illustrates the effect of drying of the treatedcellulosic material.

An aqueous solution of a reaction product of one mol proportion oftetrakis(hydroxymethyl)phosphonium chloride, 0.8 mol proportion ofammonia and 0.5 mol proportion of urea was prepared as described inExample 1 above. Samples of cotton poplin were treated with thissolution and the treated material passes through squeeze rolls adjustthe wet pick-up to about 100 percent of the solution on the weight ofthe fabric. The wet cloth was then dried for various times in a 120degree oven to obtain cloth samples with various amounts of retainedmoisture. The dried cloth was then cured by immersion in dilute aqueousammonia, scoured and conditioned as described in Example 1 above. Theseveral treated cloth samples were evaluated for flame retardance andthe data obtained is set out in the following Table V.

TABLE V Moisture retention I% 75% 50% 25% (not dried) Reaction producton scoured sample 20.6 20.6 21.5 22.3 Leaching slight slight None NoneChar length initial (in) 4.1 3.9 3.9 3.8 After boil cycles (in) 5.3 5.14.8 4.l After 9 boil cycles (in) 6.0 B 7.0 4.9 Gurley stiffness (mg) 3339 40 47 These results indicate that the undried or only slightly driedtreated material (75 percent moisture re- -tention) gives some leachingof the phosphorous containing resin material in the curing bath, andthough initially flame retardant, this characteristic is notconsistently permanent. Durable flame-retardancy is obtained when thetreated fabric is dried to about a 50 percent or less moistureretention.

The invention has been described in specific terms and the best mode forcarrying it out has been indicated. It will be apparent to those skilledin this art that numerous variations of these details can be madewithout departing from the spirit of the invention and that suchvariations are to be included within the scope of the invention.

What is claimed is:

l. The process for preparing flame retardant cellulosic containingmaterials which comprises the steps of treating a cellulosic containingmaterial with an aqueous solution of a further polymerizable methylolphosphorus compound obtained by reacting a tetrakis(hydroxymethyl)phosphonium acid salt with from about 0.5 to about 1.5mol proportion of ammonia in said aqueous solution in the presence of atleast about 0.25 mol proportion of a carbamic acid derivative selectedfrom the group consisting of urea, thiourea, biuret, guanidine,cyanamide, dicyanamide and ethyleneurea and adjusting the pH of theresultant solution to above about 1 but below about 8 below and contacting the treated material with an aqueous solution of ammonia to cureth methylol phosphorus compound in and on the cellulosic containingmaterial.

2. The process of claim 1 wherein thetetrakis(hydroxymethyl)-phosphonium acid salt is the chloride.

3. The process of claim 2 wherein the methylolphosphorus compound is theproduct of the reaction of about one mol proportion oftetrakis-(hydroxymethyl)- phosphonium chloride with about one molproportion of ammonia, in the presence of at least about 0.25 molproportion of a carbamic acid derivative.

4. The process of claim 3 wherein the treated material is dried to about50 percent or less moisture retention without substantial fixation ofthe reaction product on the fiber.

5. The process of claim 1 wherein the carbamic acid derivative is ureaor thiourea.

6. The process of claim 5 wherein the carbamic acid derivative is ureaand is present in the amount of from about 0.5 to about 2 mol proportionper mol proportion of the tetrakis(hydrox methyl)phosphonium acid salt.

7. The process of claim 5 wherein the reaction product is formed byreacting one mol proportion of tetrakis(hydroxymethyl) phosphoniumchloride with about 0.8 mol proportion of ammonia and about 0.5

mol proportion of urea.

8. Fire retardant cellulosic containing material obtained by treatingcellulosic containing material with an aqueous solution of the reactionproduct of a tetrakis(- hydroxymethyl)phosphonium acid salt with fromabout 0.5 to about 1.5 mol proportion of ammonia in said aqueoussolution and at least about 0.25 mol proportion of a carbamic acidderivative selected from the group consisting of urea, thiourea, biuret,guanidine, cyanamide, dicyanamide, and ethyleneurea, said aqueoussolution having a pH of above about 1 but below about 8 and treating thematerial with an aqueous solution of ammonia to cure said phosphoniumacid salt in and on the cellulose containing material.

v about onemol proportion of ammonium and about 0.5 mol proportion ofurea.

11. The material as claimed in claim 10 wherein thetetrakis-(hydroxymethyl)phosphonium acid salt is the 10. The material asclaimed in claim 8 wherein the 5 chloride.

reaction product is the product of the reaction of atetrakis(hydroxymethyl)-phosphonium acid salt with Po-wfio "UNITEDSTATES PATENT OFFICE v v E 5 9 CERTIFICATE OF CORRECTION Patent No.134,355 Dated Januagy 8. 197A inveflt 'w) George M. Wagner It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 1 line 54 "very low" should read ---very slow-. Column 5 line 39,"materials was" should read -material -was--; line ,67 "Sample;" shouldread -Samples-,. Column 8 line 28, "8 below" should read ---8--; line 30"cure th" should read ---cure.the--.

Signed and eealed this llth day or June 1971;; C T

(SEAL) A ttest:

EDWARD M.FLE1CHER,JR. C. MARSHALL DANN,

attesting Officer Commissioner of Patents

2. The process of claim 1 wherein thetetrakis(hydroxymethyl)-phosphonium acid salt is the chloride.
 3. Theprocess of claim 2 wherein the methylol-phosphorus compound is theproduct of the reaction of about one mol proportion oftetrakis-(hydroxymethyl)phosphonium chloride with about one molproportion of ammonia, in the presence of at least about 0.25 molproportion of a carbamic acid derivative.
 4. The process of claim 3wherein the treated material is dried to about 50 percent or lessmoisture retention without substantial fixation of the reaction producton the fiber.
 5. The process of claim 1 wherein the carbamic acidderivative is urea or thiourea.
 6. The process of claim 5 wherein thecarbamic acid derivative is urea and is present in the amount of fromabout 0.5 to about 2 mol proportion per mol proportion of thetetrakis(hydrox methyl)phosphonium acid salt.
 7. The process of claim 5wherein the reaction product is formed by reacting one mol proportion oftetrakis(hydroxymethyl) phosphonium chloride with about 0.8 molproportion of ammonia and about 0.5 mol proportion of urea.
 8. Fireretardant cellulosic containing material obtained by treating cellulosiccontaining material with an aqueous solution of the reaction product ofa tetrakis(hydroxymethyl)phosphonium acid salt with from about 0.5 toabout 1.5 mol proportion of ammonia in said aqueous solution and atleast about 0.25 mol proportion of a carbamic acid derivative selectedfrom the group consisting of urea, thiourea, biuret, guanidine,cyanamide, dicyanamide, and ethyleneurea, said aqueous solution having apH of above about 1 but below about 8 and treating the material with anaqueous solution of ammonia to cure said phosphonium acid salt in and onthe cellulose containing material.
 9. The material as claimed in claim 8wherein the treated material is drieD to a moisture retention of about50 percent by weight or less before treating the material with aqueousammonia.
 10. The material as claimed in claim 8 wherein the reactionproduct is the product of the reaction of atetrakis(hydroxymethyl)-phosphonium acid salt with about one molproportion of ammonium and about 0.5 mol proportion of urea.
 11. Thematerial as claimed in claim 10 wherein thetetrakis-(hydroxymethyl)phosphonium acid salt is the chloride.